Thermostatic mixing valves (TMVs) are well established and serve to provide a fluid (e.g., water) supply at a desired temperature. TMVs, also referred to as temperature-activated mixing valves, have a temperature responsive thermostat element, or thermal motor, operatively coupled to a valve member controlling fluid flows through hot and cold inlet ports of the valve. The mixed fluids are caused to impinge upon the thermal motor, which in turn expands and contracts and controls the relative proportions of hot and cold fluids passing through the valve. Consequently, when there is an undesirable rise in the temperature of the mixed fluid the thermal motor expands to cause the valve member to reduce the hot flow via the hot inlet port and increase the cold flow via the cold inlet port. Expansion of the thermal motor, therefore, restores the fluid supply temperature condition to that desired, with a converse operation when there is contraction of the thermal motor due to a fall in the mixed fluid temperature.
Large bore TMVs for hot water distribution systems are used to supply hot water for multiple outlets or faucets, such as groups of showers, washbasins, or baths. Large bore TMVs, which are also referred to as master mixing valves, are different than smaller, point-of-use TMVs, in that the large bore TMVs must be capable of passing substantial amounts of properly mixed water when a number of outlets are being used simultaneously. The internal arrangement of the large bore TMV, therefore, is designed such that the high flow rate can be passed without an unduly high-pressure drop. Thus, as its name implies, a large bore TMV is provided with relatively large internal passages to avoid causing any restriction to the mixed water flow under the maximum demand.
There are, however, drawbacks with large bore TMVs, such as achieving sufficient mixing of hot and cold water across a range of flow rates. When there is a low demand for mixed water the velocity of the hot and cold-water streams passing through the large bore TMV drops and is insufficient to mix the two streams fully. The result is that the streams may become laminar and mixing of the hot and cold supplies does not take place. If this happens, then the water surrounding the thermal motor is not fully mixed and as a result the thermal motor may receive a false signal.
One known approach for supplying multiple outlets is to provide a small bore TMV in parallel with a large bore TMV in combination with a pressure reducing valve or some other throttling device on the outlet of the large bore TMV. Thus, when there is a low demand for mixed water the hot and cold streams only pass through the small bore TMV. This approach, however, requires extra hardware in the form of two TMVs and a throttling device and, is therefore, more expensive and requires additional installation steps and maintenance. In addition, temperature regulation is more complicated due to its dependence on the function of two individual TMV thermal motor characteristics.
U.S. Pat. No. 6,604,687 provides another approach and discloses a high flow rate TMV that provides more accurate control of the valve outlet temperature in a low flow rate environment. The valve utilizes a flow-directing element that restricts the flow of water through the valve at low pressures and directs the flow of water toward the thermal motor, such that low flow rates are accommodated. The flow-directing element encircles the thermal motor and is formed from a flexible material so that it expands under pressure of water flowing through the valve, such that high flow rates are accommodated. At no time, however, is excess flow directed so that that it bypasses a “sensing chamber” surrounding the thermal motor.
U.S. Pat. No. 6,820,816, in contrast, provides a TMV for operation across a range of flow rates, wherein excess flow is directed so that that it does bypasses the sensing chamber surrounding the thermal motor. During low flow rate, or normal, operation, check valves in the TMV remain closed so the only pathway mixed water can follow is through the sensing chamber to a discharge portion and out the mixed water outlet. During high flow rate operation the check valves open and allow the mixed water to bypass the sensing chamber and flow directly to the discharge portion and out through the mixed water outlet.
What is still desired is a new and improved thermostatic mixing valve. Preferably the thermostatic mixing valve will be adapted to accommodate a wide range of flows yet will not allow excess flow due to a high-flow rate to bypass a sensing chamber surrounding a thermal motor of the valve.
In addition, what is also desired is an improved thermostatic mixing valve that is adapted to accommodate low and high flow rates while maintaining accurate flow temperature outputs to the thermal motor.